jim hamblen
Plays audio samples from an array stored in flash. Values are from an audio *.wav file that was automatically converted to a C array data source file. 8-bit samples used in this version and a PWM output pin (instead of AnalogOut)
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flash_audio_player_8bit
by 
jim hamblen
See https://os.mbed.com/users/4180_1/notebook/using-flash-to-play-audio-clips/ for instructions
Diff: main.cpp
- Revision:
- 2:9d7fa7666ee4
- Parent:
- 1:bd7bef7df00b
--- a/main.cpp Sun Oct 22 16:12:03 2017 +0000
+++ b/main.cpp Sun Oct 22 16:50:32 2017 +0000
@@ -1,9 +1,9 @@
#include "mbed.h"
-AnalogOut speaker(p18);
+PwmOut speaker(p26);
Ticker sampletick;
DigitalOut myled(LED1);
//Plays Audio Clip using Array in Flash
-//8-bit audio samples used
+//8-bit audio samples used on PWM pin
//setup const array in flash with audio values
//from free wav file conversion tool at
//http://ccgi.cjseymour.plus.com/wavtocode/wavtocode.htm
@@ -14,19 +14,11 @@
//get and set the frequency from wav conversion tool GUI
int i=0;
-union short_or_char {
- short s;
- char c[2];
-};
-
-union short_or_char sample;
-
-
//interrupt routine to play next audio sample from array in flash
void audio_sample ()
{
- sample.c[1] = sound_data[i];
- speaker.write_u16(sample.s);
+
+ speaker = sound_data[i]/255.0;//scale to 0.0 to 1.0 for PWM
i++;
if (i>= NUM_ELEMENTS) {
i = 0;
@@ -36,7 +28,7 @@
}
int main()
{
- sample.c[0] = 0; //setup fast byte to short conversion using union
+ speaker.period(1.0/250000.0); //PWM freq >10X audio sample rate
while(1) {
myled = 1;
//use a ticker to play send next audio sample value to D/A